Aluminum alloy brazing sheet and method for producing the same

ABSTRACT

An aluminum alloy brazing sheet achieves a stable brazability equal to by brazing using a flux, even if an etching treatment is not performed on the brazing site. The aluminum alloy brazing sheet is used to braze aluminum in an inert gas atmosphere without using a flux and includes a core material and a filler metal, one side or each side of the core material being clad with the filler metal, the core material being formed of an aluminum alloy that includes 0.2 to 1.3 mass % of Mg, the filler metal including 6 to 13 mass % of Si and 0.004 to 0.1 mass % of Li, with the balance being aluminum and unavoidable impurities, a surface oxide film having been removed from the brazing sheet, and an oil solution that decomposes when heated at 380° C. or less in an inert gas having been applied to the brazing sheet.

This is a divisional of prior U.S. application Ser. No. 14/340,081,filed Jul. 24, 2014.

TECHNICAL FIELD

The invention relates to an aluminum alloy brazing sheet and a methodfor producing the same.

BACKGROUND OF THE INVENTION

A brazing method has been widely used as a method for joining partshaving a large number of small joints (e.g., aluminum heat exchanger andmachine parts). When brazing aluminum (including an aluminum alloy), itis indispensable to break the oxide film that covers the surface of thematerial so that the molten filler metal comes in contact with thematrix or another molten filler metal. The oxide film may be broken byutilizing a method that utilizes flux or a vacuum heating method. Thesemethods have been put to practical use.

The brazing method has been applied to various fields. The brazingmethod has been most typically applied to automotive heat exchangers.Most automotive heat exchangers (e.g., radiator, heater, condenser, andevaporator) are made of aluminum, and produced by applying the brazingmethod. A method that applies a non-corrosive flux to the material,followed by heating in nitrogen gas is most widely used at present.

In recent years, a heat exchanger provided with electronic parts (e.g.,inverter cooler) has been used along with a change in driveline (e.g.,electric car and hybrid car), and a flux residue has posed problems.Therefore, some of the inverter coolers are produced using a vacuumbrazing method that does not utilize flux. However, since the vacuumbrazing method utilizes a heating furnace that increases the equipmentand maintenance costs, and has problems as to productivity and brazingstability, a brazing method that is implemented in a nitrogen gasfurnace without using flux has been increasingly desired.

For example, a method that utilizes a brazing sheet that is clad with afiller metal to which a small amount of Be is added, and performs anetching treatment in an acid or an alkali, followed by heating forbrazing was put to practical use. However, the application range of thismethod was limited, and this method is rarely used at present. Theapplication range of this method was limited for the following reasons.

(1) Since brazability is poor as compared with the method that applies aflux, a brazing failure easily occurs.

(2) A toxic element (i.e., Be) is included in the filler metal, even ina small amount.

The problem (1) is a fundamental problem. For example, even if easybrazing (e.g., brazing a fin and a tube) can be performed without aproblem, it may be difficult to reliably braze an area where it isnecessary to prevent leakage (e.g., an area in which a tube is insertedinto a header, or a joint at the outer circumference of a hollow heatexchanger formed using a pressed sheet). Therefore, the applicationrange is limited to a heat exchanger that can be easily brazed (e.g., astacked-type heat exchanger that is mainly brazed in a plane, or a heatsink that is produced by brazing a fin to a base such as an extrudedshape). The problem (2) (i.e., the toxicity of Be) is serious in thefields of food, medical equipment, and automotive heat exchangers, andthe above method may generally be rejected for this reason.

In order to solve the above problems, the inventors of the inventionproposed a brazing sheet in which a filler metal includes 0.004 to 0.1%of Li (see Japanese Patent Application No. 2012-105797). However, it wasfound through further studies that the surface oxide film must beremoved from the brazing sheet by an etching treatment before heatingfor brazing in order to uniformly braze a heat exchanger having acomplex joint structure.

Specifically, when producing a heat exchanger in which different jointsare present at a short distance using a brazing method that utilizes aflux, the oxide film is broken and removed due to the flux, and a filletis uniformly formed at each joint (i.e., the filler metal does notunevenly flow between the joints). However, the molten filler metal isdrawn toward each joint when using a brazing method that does notutilize a flux. As a result, the molten filler metal is preferentiallydrawn in the direction in which a fillet is easily formed (i.e., thefiller metal unevenly flows), and a brazing failure easily occurs atsome joints.

Therefore, in order to implement a brazability equal to that achieved bybrazing using flux when implementing brazing without using flux, it isnecessary to remove the oxide film via an etching treatment beforeheating for brazing. However, since the etching treatment has a problemin connection with waste disposal, and waste management/disposalincreases the cost, it is generally desired to avoid the etchingtreatment on the brazing site. This problem may be solved by shipping amaterial that has been subjected to the etching treatment on thematerial production site. However, the etching effects may be lostduring storage, and a decrease in brazability may occur. (JapanesePatent No. 994051, JP-A-11-285817)

SUMMARY OF THE INVENTION

The invention was conceived as a result of clarifying a factor by whichthe effect of the etching treatment is lost, and finding a techniquethat can eliminate the factor in order to solve the above problem thatoccurs in connection with the etching treatment. An object of theinvention is to provide an aluminum alloy brazing sheet that makes itpossible to implement a stable brazability equal to that achieved bybrazing using a flux, even if the etching treatment is not performed onthe brazing site, and a method for producing the same.

The invention is summarized as follows.

(1) An aluminum alloy brazing sheet for brazing aluminum in an inert gasatmosphere without using flux, the brazing sheet including a corematerial and a filler metal, one side or each side of the core materialbeing clad with the filler metal, the core material being formed of analuminum alloy that includes 0.2 to 1.3 mass % (hereinafter may bereferred to as “%”) of Mg, with the balance being aluminum andunavoidable impurities, the filler metal including 6 to 13% of Si and0.004 to 0.1% of Li, with the balance being aluminum and unavoidableimpurities, a surface oxide film having been removed from the brazingsheet, and an oil solution that decomposes when heated at 380° C. orless in an inert gas having been applied to the brazing sheet.

(2) An aluminum alloy brazing sheet for brazing aluminum in an inert gasatmosphere without using flux, the brazing sheet including a corematerial formed of an aluminum alloy (including aluminum), a fillermetal, and an intermediate material, one side or each side of the corematerial being clad with the filler metal through the intermediatematerial, the filler metal including 6 to 13% of Si and 0.004 to 0.1% ofLi, with the balance being aluminum and unavoidable impurities, theintermediate material being formed of an aluminum alloy that includes0.2 to 1.3% of Mg, with the balance being aluminum and unavoidableimpurities, a surface oxide film having been removed from the brazingsheet, and an oil solution that decomposes when heated at 380° C. orless in an inert gas having been applied to the brazing sheet.

(3) An aluminum alloy brazing sheet for brazing aluminum in an inert gasatmosphere without using flux, the brazing sheet including a corematerial, a filler metal, and a sacrificial anode material, one side ofthe core material being clad with the filler metal, the other side ofthe core material being clad with the sacrificial anode material, thecore material being formed of an aluminum alloy that includes 0.2 to1.3% of Mg, with the balance being aluminum and unavoidable impurities,the filler metal including 6 to 13% of Si and 0.004 to 0.1% of Li, withthe balance being aluminum and unavoidable impurities, the sacrificialanode material including 0.9 to 6% of Zn, with the balance beingaluminum and unavoidable impurities, a surface oxide film having beenremoved from the brazing sheet, and an oil solution that decomposes whenheated at 380° C. or less in an inert gas having been applied to thebrazing sheet.

(4) An aluminum alloy brazing sheet for brazing aluminum in an inert gasatmosphere without using flux, the brazing sheet including a corematerial formed of an aluminum alloy or aluminum, a filler metal, anintermediate material, and a sacrificial anode material, one side of thecore material being clad with the filler metal through the intermediatematerial, the other side of the core material being clad with thesacrificial anode material, the intermediate material being formed of analuminum alloy that includes 0.2 to 1.3% of Mg, with the balance beingaluminum and unavoidable impurities, the filler metal including 6 to 13%of Si and 0.004 to 0.1% of Li, with the balance being aluminum andunavoidable impurities, the sacrificial anode material including 0.9 to6% of Zn, with the balance being aluminum and unavoidable impurities, asurface oxide film having been removed from the brazing sheet, and anoil solution that decomposes when heated at 380° C. or less in an inertgas having been applied to the brazing sheet.

(5) The aluminum alloy brazing sheet according to (1) or (3), whereinthe aluminum alloy that forms the core material includes 0.2 to 1.3% ofMg, and one or more elements from among 0.5 to 1.8% of Mn, 1.0% or lessof Si, 1.0% or less of Fe, 0.5% or less of Cu, 0.5% or less of Zn, 0.2%or less of Ti, and 0.5% or less of Zr, with the balance being aluminumand unavoidable impurities.

(6) The aluminum alloy brazing sheet according to (2) or (4), whereinthe aluminum alloy that forms the intermediate material includes 0.2 to1.3% of Mg, and one or more elements from among 0.5 to 1.8% of Mn, 1.0%or less of Si, 1.0% or less of Fe, 0.5% or less of Cu, 0.5% or less ofZn, 0.2% or less of Ti, and 0.5% or less of Zr, with the balance beingaluminum and unavoidable impurities.

(7) The aluminum alloy brazing sheet according to (2) or (4), whereinthe aluminum alloy that forms the core material includes 0.5 to 1.8% ofMn, and one or more elements from among 1.0% or less of Si, 1.0% or lessof Fe, 0.5% or less of Cu, 0.5% or less of Zn, 0.2% or less of Ti, and0.5% or less of Zr, with the balance being aluminum and unavoidableimpurities.

(8) The aluminum alloy brazing sheet according to (6), wherein thealuminum alloy that forms the core material includes 0.5 to 1.8% of Mn,and one or more elements from among 1.0% or less of Si, 1.0% or less ofFe, 0.5% or less of Cu, 0.5% or less of Zn, 0.2% or less of Ti, and 0.5%or less of Zr, with the balance being aluminum and unavoidableimpurities.

(9) The aluminum alloy brazing sheet according to (1) or (3), whereinthe filler metal further includes one or more elements from among 0.004to 0.2% of Bi, 0.05 to 0.4% of Mg, 0.002 to 0.05% of Sr, 0.003 to 0.07%of Sb, 0.05 to 0.8% of Fe, 0.05 to 0.2% of Mn, and 0.01 to 0.15% of Ti.

(10) The aluminum alloy brazing sheet according to (2) or (4), whereinthe filler metal further includes one or more elements from among 0.004to 0.2% of Bi, 0.05 to 0.4% of Mg, 0.002 to 0.05% of Sr, 0.003 to 0.07%of Sb, 0.05 to 0.8% of Fe, 0.05 to 0.2% of Mn, and 0.01 to 0.15% of Ti.

(11) The aluminum alloy brazing sheet according to (5), wherein thefiller metal further includes one or more elements from among 0.004 to0.2% of Bi, 0.05 to 0.4% of Mg, 0.002 to 0.05% of Sr, 0.003 to 0.07% ofSb, 0.05 to 0.8% of Fe, 0.05 to 0.2% of Mn, and 0.01 to 0.15% of Ti.

(12) The aluminum alloy brazing sheet according to (6), wherein thefiller metal further includes one or more elements from among 0.004 to0.2% of Bi, 0.05 to 0.4% of Mg, 0.002 to 0.05% of Sr, 0.003 to 0.07% ofSb, 0.05 to 0.8% of Fe, 0.05 to 0.2% of Mn, and 0.01 to 0.15% of Ti.

(13) The aluminum alloy brazing sheet according to (7), wherein thefiller metal further includes one or more elements from among 0.004 to0.2% of Bi, 0.05 to 0.4% of Mg, 0.002 to 0.05% of Sr, 0.003 to 0.07% ofSb, 0.05 to 0.8% of Fe, 0.05 to 0.2% of Mn, and 0.01 to 0.15% of Ti.

(14) The aluminum alloy brazing sheet according to (8), wherein thefiller metal further includes one or more elements from among 0.004 to0.2% of Bi, 0.05 to 0.4% of Mg, 0.002 to 0.05% of Sr, 0.003 to 0.07% ofSb, 0.05 to 0.8% of Fe, 0.05 to 0.2% of Mn, and 0.01 to 0.15% of Ti.

(15) A method for producing the aluminum alloy brazing sheet accordingto any one of (1) to (14), the method including cleaning a brazing sheetproduced by rolling with an acid to remove a surface oxide film, andapplying an oil solution that decomposes when heated at 380° C. or lessin an inert gas to the brazing sheet.

(16) The method according to (15), wherein the cleaning with the acidetches a surface of the brazing sheet to a depth of 5 nm or more.

(17) The method according to (15) or (16), wherein the oil solution thatdecomposes when heated at 200 to 380° C. in an inert gas is applied tothe brazing sheet in an amount of 500 mg/m² or more.

These aspects of the invention thus provide an aluminum alloy brazingsheet that makes it possible to implement a stable brazability equal tothat achieved by brazing using a flux, even if an etching treatment isnot performed on the brazing site, and a method for producing the same.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a clearance filling test specimen thatutilizes a sheet material as a vertical material.

FIG. 2 is a view illustrating the relationship between the holding timein a thermo-hygrostat and the clearance filling length.

FIG. 3 is a view illustrating the relationship between the holding timein a thermo-hygrostat and the clearance filling length when dewcondensation was caused to occur once a day.

FIG. 4 is a view illustrating the external appearance of a cup testspecimen.

FIG. 5 is a view illustrating the state of a cup test specimen duringbrazing.

FIG. 6 is a view illustrating a clearance filling test specimen thatutilizes a tube material as a vertical material.

DESCRIPTION OF EMBODIMENTS

In order to implement brazing in an inert gas atmosphere without using aflux, it is necessary to implement (1) a function of promoting thebreakage of an oxide film, and (2) a function of reducing the surfacetension of a molten filler metal by means of a material. Opinions aredivided on the mechanism by which the flux achieves the function (1). Itis most likely that the molten flux enters cracks formed in the oxidefilm (i.e., cracks that occur due to the difference in thermal expansionfrom the matrix), and removes the oxide film from aluminum.

Molten flux can enter the cracks formed in the oxide film, and removethe oxide film from aluminum since the molten flux has a highwettability with the oxide film (Al₂O₃). The flux is used to remove anoxide when casting aluminum due to a high wettability with an oxide.When a small amount of Be is added to the filler metal, Be is diffusedover the surface of the filler metal during heating for brazing, andforms BeO on the surface of the filler metal (confirmed by TEMobservation). Since Be locally removes oxygen from Al₂O₃, the unity ofthe oxide film deteriorates, and cracks that occur due to the differencein thermal expansion from the matrix become fine. It is considered thatthe flow of the molten filler metal is thus promoted. An Al—Si fillermetal to which about 0.01% of Be is added exhibits a wettability with analuminum material even when a flux is not applied due to the above oxidefilm breakage function.

An element having a free energy of formation of oxides that is equal toor less than that of Al₂O₃ achieves the oxide film breakage function.Examples of a practical element other than Be include Mg, Ca, Ce, Zr,Sr, Ba, and the like. Since Mg has a special effect (described later),it is desirable to use Mg taking account of the special effect. Theinventors proposed the use of Ca, Ce, and Zr (see Japanese PatentApplication No. 2011-275285), and confirmed that a fillet is formed on apractical joint due to the combined effect with Mg. However, it wasfound that it is difficult to achieve a stable effect comparable to thatof Be when brazing a joint with a high degree of difficulty in brazing.Sr has a low free energy of formation of oxides. However, Sr achievesthe oxide film breakage effect to only a small extent when added alone.

In view of the above situation, the inventors focused on Li. The freeenergy of formation of Li₂O at 600° C. is −970 kJ/mol, which is almostequal to that (−952 kJ/mol) of Al₂O₃. Since pure Li metal produces acombustible/flammable gas that may ignite upon contact with water, it isdifficult to handle pure Li metal (e.g., it is necessary to immerse pureLi metal in oil during storage). Therefore, Li was excluded fromcandidates for an additional element. However, it was found that castingcan be safely and easily performed by producing an intermediate alloywith aluminum using a special method. An Al—Si alloy and an Al—Liintermediate alloy were cast, and an Al—Si filler metal to which a smallamount of Li was added was produced. A spreading test was performedusing the resulting products. As a result, it was found that it ispossible to obtain a wettability equal to or higher than that of anAl—Si filler metal to which a small amount of Be is added.

However, when Li is merely added to an Al—Si filler metal, a practicaljoining capability such as a clearance filling capability cannot beobtained in the same manner as in the case of adding Be. This isprimarily because the function of a flux that removes an oxide film fromaluminum cannot be achieved when Li or Be is added. It is physicallydifficult to achieve the function of removing an oxide film fromaluminum by adding an element to the filler metal. However, it ispossible to improve the brazability by forming an Al₂MgO₄ spinel-typecompound in an Al₂O₃ oxide film so that the oxide film becomes fragile.

Al₂MgO₄ can be formed in the oxide film by adding Mg to the fillermetal. However, it is preferable to add Mg to the core material or theintermediate material provided between the core material and the fillermetal in order to prevent a situation in which MgO that impairsbrazability is formed on the surface of the filler metal during materialproduction and heating for brazing. When Mg is added to the corematerial or the intermediate material, Mg slowly diffuses inside thefiller metal during heating for brazing, and rapidly diffuses toward thesurface of the filler metal when the filler metal is melted (i.e.,partial melting of an Al—Si—Mg ternary eutectic). Therefore, it ispossible to form Al₂MgO₄ in the Al₂O₃ oxide film without forming MgO onthe surface of the filler metal, and reliably cause the oxide film tobecome fragile.

Since Mg has an effect of reducing the surface tension of the moltenfiller metal (described later), it is effective to add Mg to the corematerial or the intermediate material in order to improve thefillet-forming capability when producing a practical joint. It iseffective to reduce the surface tension of the molten Al—Si filler metalin order to reliably form a fillet on a practical joint having aclearance in a state in which the wettability of the molten filler metalis improved by breaking the oxide film (or removing the oxide film, orcausing the oxide film to become fragile). It is also effective to addBi in order to reduce the surface tension of the molten filler metal.

It is effective to improve the fluidity of the filler metal in order tofurther improve the fillet-forming capability without increasing theamount of the filler metal and the Si concentration in the filler metal.It is effective to reduce the particle size of Si in the Al—Si fillermetal in order to improve the fluidity of the filler metal. The additionof Sr or Sb is a practical means. Na also has an effect of refining Siparticles. However, since the handling of Na is very difficult, Na isnot suitable for practical use.

When producing a heat exchanger by brazing, a molten filler metal maymove downward due to the effects of gravity, and may not be sufficientlysupplied to an upper joint. In particular, the effects of gravity cannotbe disregarded when a joint requires a large amount of filler metal. Itis effective to increase the viscosity of the molten filler metal inorder to reduce the effects of gravity. Fe, Mn, and Ti are effective forincreasing the viscosity of the molten filler metal. These elements andprecipitates of compounds thereof increase the viscosity of the moltenfiller metal, and reduce the effects of gravity.

According to several embodiments of the invention, an aluminum alloybrazing sheet is used for brazing aluminum in an inert gas atmospherewithout using a flux. The material configuration of the aluminum alloybrazing sheet is described below. In a first embodiment, the brazingsheet includes a core material and a filler metal, one side or each sideof the core material being clad with the filler metal, the core materialbeing formed of an aluminum alloy that includes 0.2 to 1.3% of Mg, andthe filler metal including 6 to 13% of Si and 0.004 to 0.1% of Li, withthe balance being aluminum and unavoidable impurities. In a secondembodiment, the brazing sheet includes a core material formed of analuminum alloy (including aluminum), a filler metal, and an intermediatematerial, one side or each side of the core material being clad with thefiller metal through the intermediate material, the filler metalincluding 6 to 13% of Si and 0.004 to 0.1% of Li, with the balance beingaluminum and unavoidable impurities, and the intermediate material beingformed of an aluminum alloy that includes 0.2 to 1.3% of Mg.

The above Si content (6 to 13%) is a practical range for the fillermetal. If the Si content is less than 6%, the filler metal may notachieve a sufficient function since the amount of the filler metal maybe insufficient, and the fluidity of the filler metal may deteriorate.If the Si content exceeds 13%, the matrix may melt to a large extent dueto excessive filler metal, and coarse primary Si crystals may be easilyformed in the filler metal. As a result, a hole may be formed due tomelting during brazing.

If the Li content is less than 0.004%, the effect of breaking the oxidefilm may be insufficient. If the Li content exceeds 0.1%, Li₂O may beunnecessarily formed, and the brazability may deteriorate. If the Mgcontent in the core material and the intermediate material is less than0.2%, the effect of breaking the oxide film may be insufficient. If theMg content in the core material and the intermediate material exceeds1.3%, the melting point of the core material and the intermediatematerial may decrease, and it may be difficult to implement brazing.

In a third embodiment, the brazing sheet includes the core material, thefiller metal, and a sacrificial anode material, one side of the corematerial being clad with the filler metal, the other side of the corematerial being clad with the sacrificial anode material, and thesacrificial anode material including 0.9 to 6% of Zn, with the balancebeing aluminum and unavoidable impurities. If the Zn content in thesacrificial anode material is less than 0.9%, the sacrificial anodeeffect may be insufficient. If the Zn content in the sacrificial anodematerial exceeds 6%, the corrosion rate may increase, and the corrosionlifetime may decrease.

Bi and Mg have an effect of reducing the surface tension of the fillermetal when added either alone or in combination. If the Bi content isless than 0.004%, the effect of reducing the surface tension of thefiller metal may be insufficient. If the Bi content exceeds 0.2%, thefiller metal may be significantly colored, and an improvement inbrazability may not be achieved. If the Mg content is less than 0.05%,the effect of reducing the surface tension of the filler metal may beinsufficient. If the Mg content exceeds 0.4%, MgO may be formed on thesurface of the filler metal, and may impair brazability.

Sr and Sb have an effect of refining the Al—Si eutectic structure of thefiller metal when added either alone or in combination. If the Srcontent is less than 0.002%, the effect of refining the Al—Si eutecticstructure of the filler metal may be insufficient. If the Sr contentexceeds 0.05%, the effect of refining the Al—Si eutectic structure ofthe filler metal may be saturated, and the filler metal production costmay increase. If the Sb content is less than 0.003%, the effect ofrefining the Al—Si eutectic structure of the filler metal may beinsufficient. If the Sb content exceeds 0.07%, the clearance fillingcapability may be adversely affected.

Fe, Mn, and Ti have an effect of increasing the viscosity of the moltenfiller metal when added either alone or in combination. The Fe content,the Mn content, and the Ti content are preferably 0.05 to 0.8%, 0.05 to0.2%, and 0.01 to 0.15%, respectively. If the Fe content, the Mncontent, or the Ti content is less than the lower limit, the effect ofincreasing the viscosity of the molten filler metal may be insufficient.If the Fe content, the Mn content, or the Ti content exceeds the upperlimit, the fluidity of the molten filler metal may be adverselyaffected.

The core material and the intermediate material that include 0.2 to 1.3%of Mg may include one or more elements from among Mn, Si, Fe, Cu, Zn,Ti, and Zr in order to control the strength, the corrosion resistance,the structure, and the like of the core material and the intermediatematerial. Mn is effective for improving the strength and adjusting thepotential of the material. If the Mn content is less than 0.5%, theeffect of improving the strength of the material may be insufficient. Ifthe Mn content exceeds 1.8%, cracks may easily occur when rolling thematerial. Si is effective for improving the strength of the material. Ifthe Si content exceeds 1.0%, the melting point of the material maydecrease, and the brazability may be adversely affected. Fe is effectivefor improving the strength of the material. If the Fe content exceeds1.0%, the corrosion resistance of the material may be adverselyaffected, and coarse precipitates may be easily produced.

Cu is effective for improving the strength and adjusting the potentialof the material. If the Cu content exceeds 0.5%, intergranular corrosionmay easily occur, and the melting point of the material may decrease. Znis effective for adjusting the potential of the material. If the Zncontent exceeds 0.5%, the natural electrode potential may decrease to alarge extent, and the corrosion perforation lifetime may decrease. Ti iseffective for causing corrosion to proceed in layers. If the Ti contentexceeds 0.2%, coarse precipitates may be easily produced. Zr iseffective for increasing the crystal grain size of the material. If theZr content exceeds 0.5%, cracks may easily occur when producing thematerial.

In the brazing sheet according to the second embodiment, aluminum or analuminum alloy may be used as the core material. When using an aluminumalloy as the core material, it is preferable that the aluminum alloyinclude 0.5 to 1.8% of Mn, and one or more elements from among 1.0% orless of Si, 1.0% or less of Fe, 0.5% or less of Cu, 0.5% or less of Zn,0.2% or less of Ti, and 0.5% or less of Zr, with the balance beingaluminum and unavoidable impurities. Mn is effective for improving thestrength and adjusting the potential of the material. If the Mn contentis less than 0.5%, the effect of improving the strength of the materialmay be insufficient. If the Mn content exceeds 1.8%, cracks may easilyoccur when rolling the material. Si is effective for improving thestrength of the material. If the Si content exceeds 1.0%, the meltingpoint of the material may decrease, and the brazability may be adverselyaffected. Fe is effective for improving the strength of the material. Ifthe Fe content exceeds 1.0%, the corrosion resistance of the materialmay be adversely affected, and coarse precipitates may be easilyproduced.

Cu is effective for improving the strength and adjusting the potentialof the material. If the Cu content exceeds 0.5%, intergranular corrosionmay easily occur, and the melting point of the material may decrease. Znis effective for adjusting the potential of the material. If the Zncontent exceeds 0.5%, the natural electrode potential may decrease to alarge extent, and the corrosion perforation lifetime may decrease. Ti iseffective for causing corrosion to proceed in layers. If the Ti contentexceeds 0.2%, coarse precipitates may be easily produced. Zr iseffective for increasing the crystal grain size of the material. If theZr content exceeds 0.5%, cracks may easily occur when producing thematerial.

The details of removal of the surface oxide film by etching, andapplication of the oil solution that decomposes when heated at 380° C.or less in an inert gas, are described below. The etching treatmentbreaks and removes the oxide film on the surface of the filler metal.However, a natural oxide film is formed on the surface of the fillermetal immediately after etching. Since the natural oxide film formed atroom temperature has a small thickness, and easily breaks due to thermalexpansion of the material during brazing, it is possible to implementbrazing in an inert gas without using flux by utilizing a filler metalthat includes Li.

An acid solution or an alkali solution is normally used for the etchingtreatment, and has an effect of removing the oxide film on the surfaceof the filler metal. It was found that a material washed with analkaline solution (e.g., caustic soda) shows a poor fluxless brazabilityin nitrogen gas as compared with a material washed with an acid. It isconjectured that aluminum hydroxide or sodium aluminate produced due toalkali washing decomposes during heating for brazing to release water.

A material subjected to the etching treatment using an acid (e.g., adiluted solution of hydrofluoric acid, a mixed diluted solution ofhydrofluoric acid and nitric acid, or a mixed diluted solution ofphosphoric acid and sulfuric acid) exhibits an excellent brazability. Itwas found from the analysis results for the test specimen that exhibitedan excellent brazability that the surface of the filler metal includingthe oxide film was etched to a depth of 5 to 200 nm by the etchingtreatment using an acid. It was also found that the brazability is notaffected even if the etching depth exceeds 200 nm.

The etching effects may be lost during the storage period due tomoisture in the air. An oxide film may grow when the material is storedfor a long time at a high temperature and a high humidity. In order todetermine a deterioration in the etching effects due to the growth of anoxide film during the storage period, a brazing sheet (horizontalmaterial) including a filler metal formed of an Al—10% Si—0.05%Li—0.004% Bi alloy (thickness: 40 μm), and a core material formed of anAl—0.62% Mg alloy, and a 3003 alloy material (vertical material) weredegreased, immersed in an etching solution treatment solution (2% nitricacid and 1% hydrofluoric acid) 20° C. for 90 seconds, and stored in athermo-hygrostat (temperature: 50° C., humidity: 85%) up to 2 weeks. Astorage period of 2 weeks under the above conditions corresponds to astorage period of about 2 years under normal conditions.

The clearance filling test specimen illustrated in FIG. 1 was preparedusing the material that was stored in the thermo-hygrostat for 1 day, 3days, 7 days, or 14 days, or the material immediately after the etchingtreatment, and brazed at a maximum temperature of 595° C. in a nitrogengas atmosphere. FIG. 2 shows the relationship between the holding timein the thermo-hygrostat and the clearance filling length. As shown inFIG. 2, almost no decrease in the clearance filling length was observedeven when the material was stored in the thermo-hygrostat for 2 weeks.

The materials that were subjected to the etching treatment under theabove conditions, and cooled to −10° C. in a freezer were placed in athermo-hygrostat, removed from the thermo-hygrostat every day, cooled to−10° C. in the freezer, and returned to the thermo-hygrostat (i.e., dewcondensation was caused to occur once a day). An evaluation test wasthen performed in the same manner as described above. The results areshown in FIG. 3. As shown in FIG. 3, the clearance filling lengthdecreased after 1 day due to dew condensation, and brazabilitydeteriorated after 2 weeks to such an extent that almost no fillet wasformed. A spot pattern appeared on the surface of the material, andproduction of Al(OH)₃ (aluminum hydroxide) was confirmed by chemicalanalysis. Since Al(OH)₃ changes into Al₂O₃ during heating for brazing torelease water, reoxidation of the surface of the filler metal ispromoted, and brazability deteriorates. Therefore, it is necessary toprevent dew condensation on the surface of the material during thestorage period.

Dew condensation can be prevented by air-tightly storing the material.However, since the material is frequently unpacked depending on theusage state, it is not realistic to prevent dew condensation byair-tightly storing the material. The surface of the material may beprotected so that water droplets do not adhere to the surface of thematerial even in a dew condensation environment. The surface of thematerial may be protected by painting using an oily or water-solublepaint, application of a protective sheet, application of an oilsolution, or the like. It was considered to be most effective to find anoil solution that prevents dew condensation during the storage period,and decomposes during heating for brazing (i.e., does not cause adeterioration in brazability).

The oil solution is required to have a moderate volatility (i.e.,prevent dew condensation during the storage period), and decomposeduring heating so that the brazability is not impaired. It was foundthat the above requirements are met when the oil solution decomposeswhen heated at 200 to 380° C. in an inert gas. It was also found thatthe oil solution can maintain the effects during storage for a long timeor storage in a severe environment when the oil solution is applied inan amount of 500 mg/m² or more.

It is possible to make it unnecessary to perform the etching treatmentin the brazing site by subjecting the surface of the brazing sheet tothe etching treatment in the final stage (rolling) of the production ofthe brazing sheet, and applying the oil solution so that the etchingeffects can be maintained. The etching treatment using an alkalisolution is not desirable since aluminum hydroxide or the like producedduring the etching treatment decomposes during heating for brazing torelease water. The oil solution must decompose during heating forbrazing in an inert gas so that the brazability is not adverselyaffected even if a special degreasing treatment is not performed. Ahighly volatile oil solution may be used when the material is brazedshortly after production, or when the material is air-tightly stored,and used immediately after unpacking.

If the etching depth of the surface of the filler metal including thesurface oxide film is less than 5 nm, the etching effects maydeteriorate. A highly volatile oil solution (i.e., an oil solution thatdecomposes when heated at less than 200° C. in an inert gas) may notsufficiently maintain the etching effects when the material is brazedwhen a long time has elapsed after production, or when the material isstored in an insufficient air-tight state in an environment in which achange in temperature within one day is large, or when the material isfrequently unpacked in a high-humidity environment, and usedintermittently. If an oil solution that decomposes when heated at 200°C. or more in an inert gas is applied in an amount of less than 500mg/m², the oil solution may not sufficiently maintain the etchingeffects during storage for a long time or storage in a severeenvironment.

EXAMPLES

The invention is further described below by way of examples todemonstrate the effects of the invention. Note that the followingexamples are for illustration purposes only, and the invention is notlimited to the following examples.

Example 1

A core material was produced by casting an ingot using a continuouscasting method, and facing the ingot to a given thickness. A fillermetal, an intermediate material, and a sacrificial anode material wereproduced by casting an ingot using a continuous casting method, andhot-rolling the ingot to a given thickness. The filler metal was stackedon one side of the core material, followed by hot rolling and coldrolling, or the filler metal was stacked on one side of the corematerial through the intermediate material, followed by hot rolling andcold rolling, or the filler metal was stacked on one side of the corematerial through the intermediate material, and the sacrificial anodematerial was stacked on the other side of the core material, followed byhot rolling and cold rolling to produce an aluminum alloy brazing sheethaving a thickness of 0.4 mm. The composition of the core material, thefiller metal, the intermediate material, and the sacrificial anodematerial is shown in Table 1.

The resulting aluminum alloy brazing sheet (specimens 1 to 25) wassubjected to a clearance filling test and a cup test according to thefollowing methods. The results are shown in Table 1.

Clearance Filling Test

The brazing sheet was degreased, and immersed for 90 seconds in a mixeddilution solution (2% nitric acid and 1% fluoric acid, 20° C.) (etchingtreatment). A 3003 alloy sheet (thickness: 1 mm) (vertical material) wasassembled with the brazing sheet (horizontal material) to prepare aclearance filling test specimen illustrated in FIG. 1. A nitrogen gasfurnace (double chamber furnace) including a preheating chamber(internal volume: 0.4 m³) and a brazing chamber was used. The clearancefilling test specimen was placed in the brazing chamber, and brazed at amaximum temperature of 595° C. Nitrogen gas was fed to each chamber ofthe nitrogen gas furnace at a flow rate of 20 m³/h, and the temperaturewas increased from 450° C. to 595° C. within about 12 minutes. Theoxygen concentration in the brazing chamber after completion of heatingwas 7 to 17 ppm. When the temperature of the clearance filling testspecimen placed in the brazing chamber reached 595° C., the clearancefilling test specimen was transferred to the preheating chamber, cooledto 550° C., removed from the preheating chamber, and allowed to cool inair.

Cup Test

The brazing sheets were pressed so that the filler metal was positionedon the inner side, degreased, and subjected to an etching treatment inthe same manner as described above. A 3003 alloy material (thickness:0.1 mm) that was formed in the shape of a fin and degreased, was placedtherein to prepare a cup test specimen illustrated in FIG. 4. The cuptest specimen was heated during brazing in the state illustrated in FIG.5 in order to simulate the adverse effects of gravity. The cup testspecimen was placed in the same furnace as that used for the clearancefilling test. Nitrogen gas was fed to each chamber at a flow rate of 20m³/h, and the temperature was increased from 450° C. to 595° C. withinabout 14 minutes. The oxygen concentration in the brazing chamber aftercompletion of heating was 6 to 15 ppm. When the temperature of the cuptest specimen placed in the brazing chamber reached 595° C., the cuptest specimen was transferred to the preheating chamber, cooled to 550°C., removed from the preheating chamber, and allowed to cool in air.

The clearance filling length of the clearance filling test specimen wasmeasured after brazing to evaluate the fillet-forming capability. A casewhere the clearance filling length was 25 mm or more was evaluated as“Acceptable” (practical level). The flow factor was calculated by thefollowing expression.Flow factor K=volume of fillet formed/volume of filler metal ofhorizontal material

A fillet on the upper side of the outer circumference of the cup testspecimen was observed with the naked eye and using a stereoscopicmicroscope, and evaluated as described below.

-   A: A uniform fillet was formed over the total length.-   B: A fillet was formed over the total length, but was rather small.-   C: A fillet was formed over the total length, but broke in part.-   D: A fillet broke at a plurality points.-   E: A fillet was not formed.

TABLE 1 Clearance Brazing Flow filling state on Component (mass %)Thickness factor length upper side Specimen Material Si Fe Mn Mg Zn TiLi Bi Sr Sb (μm) K (mm) of cup 1 Filler metal 10 0.004 60 0.45 28 C to BCore material 1.2 1.29 340 2 Filler metal 10 0.05 60 0.47 29 C to B Corematerial 1.2 0.20 340 3 Filler metal 10 0.10 60 0.49 31 C to B Corematerial 1.2 0.62 340 4 Filler metal 10 0.004 60 0.44 27 C to BIntermediate 1.29 50 material Core material 1.2 290 5 Filler metal 100.004 60 0.44 26 C to B Intermediate 0.20 50 material Core material 2906 Filler metal 10 0.004 60 0.45 28 C to B Intermediate 0.62 50 materialCore material 290 7 Filler metal 10 0.05 60 0.48 30 B Intermediate 0.6250 material Core material 240 Sacrificial 0.9 50 anode material 8 Fillermetal 10 0.05 60 0.44 29 B Intermediate 0.62 50 material Core material240 Sacrificial 6.0 50 anode material 9 Filler metal 10 0.05 0.004 600.47 32 B Core material 0.62 340 10 Filler metal 10 0.05 0.2 60 0.48 33B Core material 0.62 340 11 Filler metal 10 0.05 0.05 60 0.47 33 B Corematerial 0.62 340 12 Filler metal 10 0.41 0.05 60 0.47 33 B Corematerial 0.62 340 13 Filler metal 10 0.15 0.05 0.03 60 0.48 34 B Corematerial 0.62 340 Core material 0.62 340 14 Filler metal 10 0.05 0.030.002 60 0.51 36 B Core material 0.62 340 15 Filler metal 10 0.05 0.030.05 60 0.52 36 B Core material 0.62 340 16 Filler metal 10 0.05 0.030.003 60 0.51 35 B Core material 0.62 340 17 Filler metal 10 0.05 0.030.07 60 0.5 35 B Core material 0.62 340 18 Filler metal 10 0.05 0.030.006 0.009 60 0.53 37 B Core material 0.62 340 19 Filler metal 10 0.050.05 0.03 0.006 0.009 60 0.52 35 A Core material 0.62 340 20 Fillermetal 10 0.8 0.05 0.03 0.006 0.009 60 0.51 34 A Core material 0.62 34021 Filler metal 10 0.05 0.05 0.03 0.006 0.009 60 0.52 34 A Core material0.62 340 22 Filler metal 10 0.19 0.05 0.03 0.006 0.009 60 0.52 33 A Corematerial 0.62 340 23 Filler metal 10 0.01 0.05 0.03 0.006 0.009 60 0.5334 A Core material 0.62 340 24 Filler metal 10 0.15 0.05 0.03 0.0060.009 60 0.52 34 A Core material 0.62 340 25 Filler metal 10 0.4 0.090.05 0.05 0.03 0.006 0.009 60 0.52 33 A Core material 0.62 340

As shown in Table 1, when using the brazing sheets 1 to 25 according tothe invention, a fillet having a clearance filling length of 26 to 37 mmwas formed in the clearance filling test (i.e., the brazing sheets 1 to25 showed a sufficiently practical fillet-forming capability).

The clearance filling length reached the practical level when Li wasadded to the filler metal, and Mg was added to the core material(specimens 1 to 3). A similar effect was observed when Mg (that has aneffect of causing the oxide film to become fragile) was added to theintermediate material (specimens 4 to 8). A similar effect was alsoobserved when one side of the core material was clad with thesacrificial anode material (specimens 7 and 8).

When Bi or Mg was added to the filler metal, the flow factor increasedto only a small extent, but the clearance filling length increased byabout 10%, and a fillet was sufficiently formed on the upper side of theouter circumference of the cup test specimen. It is considered that theabove results were obtained since the surface tension of the moltenfiller metal decreased due to the addition of Bi or Mg (specimens 9 to13). When Sr or Sb was added to the filler metal, the flow factorincreased by 5 to 10%, and the clearance filling length also increased(specimens 14 to 18). When Fe, Mn, or Ti was added to the filler metal,a fillet was uniformly formed on the upper side of the outercircumference of the cup test specimen. It is considered that the aboveresults were obtained since the effects of gravity were canceled due toan increase in the viscosity of the molten filler metal (specimens 19 to25).

Comparative Example 1

A core material was produced by casting an ingot using a continuouscasting method, and facing the ingot to a given thickness. A fillermetal was produced by casting an ingot using a continuous castingmethod, and hot-rolling the ingot to a given thickness. The filler metalwas stacked on one side of the core material, followed by hot rollingand cold rolling to produce an aluminum alloy brazing sheet having athickness of 0.4 mm. The composition of the core material and the fillermetal is shown in Table 2.

The resulting aluminum alloy brazing sheet (specimens 26 to 45) wassubjected to the gap filling test and the cup test in the same manner asin Example 1. The results are shown in Table 2.

TABLE 2 Clearance Brazing Flow filling state on Component (mass %)Thickness factor length upper side Specimen Material Si Fe Mn Mg Zn TiLi Bi Sr Sb Be (μm) K (mm) of cup 26 Filler metal 10 60 — 6 E Corematerial 1.2 340 27 Filler metal 10 0.05 60 0.31 22 C Core material 1.2340 28 Filler metal 10 60 0.28 20 D Core material 1.2 0.62 340 29 Fillermetal 10 0.20 60 0.27 18 D Core material 1.2 340 30 Filler metal 10 0.020.01 60 0.39 25 C Core material 1.2 340 31 Filler metal 10 0.02 0.01 600.45 29 C to B Core material 1.2 0.62 340 32 Filler metal 10 0.002 600.29 20 D Core material 1.2 0.62 340 33 Filler metal 10 0.16 60 0.37 24C Core material 1.2 0.62 340 34 Filler metal 10 0.05 60 0.37 23 C Corematerial 1.2 0.11 340 35 Filler metal 10 0.02 60 — 11 D Core material1.2 340 36 Filler metal 10 0.004 0.002 60 0.38 26 C to B Core material0.62 340 37 Filler metal 10 0.004 0.25 60 0.36 24 C Core material 0.62340 38 Filler metal 10 0.02 0.004 60 0.37 25 C to B Core material 0.62340 39 Filler metal 10 0.61 0.004 60 0.35 23 C Core material 0.62 340 40Filler metal 10 0.004 0.001 60 0.38 25 C to B Core material 0.62 340 41Filler metal 10 0.004 0.07 60 0.51 35 B Core material 0.62 340 42 Fillermetal 10 0.004 0.001 60 0.38 25 C to B Core material 0.62 340 43 Fillermetal 10 0.004 0.1 60 0.33 22 C Core material 0.62 340 44 Filler metal10 0.03 0.02 0.005 0.05 0.03 0.006 0.009 60 0.52 36 B Core material 0.62340 45 Filler metal 10 1.1 0.29 0.2 0.05 0.03 0.006 0.009 60 0.41 27 Cto B Core material 0.62 340

As shown in Table 2, when using the brazing sheet produced using anAl-10% Si alloy filler metal and an Al—Mn alloy core material, theclearance filling length was 6 mm (i.e., brazability significantlydeteriorated), and almost no fillet was formed in the cup test (specimen26). Brazability was improved when Li was added to the filler metal, orwhen Mg was added to the core material, or when Mg was added to thefiller metal. In this case, however, the clearance filling length was 22mm or less (i.e., the practical level was not reached) (specimens 27 to29).

When using the brazing sheet (specimen 30) in which Bi and Be were addedto the filler metal, and the brazing sheet (specimen 31) in which Bi andBe were added to the filler metal, and Mg was added to the corematerial, a clearance filling length of 25 mm or more was obtained.However, since the filler metal includes Be (i.e., a toxic element),these brazing sheets are not suitable for practical use.

When the Li content in the filler metal was low (specimen 32), or whenthe Li content in the filler metal was high (specimen 33), the clearancefilling length was less than 25 mm. When the Mg content in the corematerial was low (specimen 34), the clearance filling length was lessthan 25 mm. When only Bi was added to the filler metal (specimen 35),the effect of breaking the oxide film was insufficient, and brazabilitywas poor.

When Li and Bi were added to the filler metal, and Mg was added to thecore material, an improvement in brazability was not observed when theBi content was low (specimen 36), and brazability decreased to someextent, and significant coloration was observed when the Bi content wastoo high (specimen 37). When Li was added to the filler metal, and Mgwas added to the core material, no effect was observed when the Mgcontent in the filler metal was low (specimen 38), and brazabilitydecreased when the Mg content in the filler metal was too high (specimen39).

When Li was added to the filler metal, and Mg was added to the corematerial, no effect was observed when the Sr content in the filler metalwas low (specimen 40), and an improvement in brazability was notobserved even when the Sr content in the filler metal was more than0.05% (specimen 41). In this case, the material cost merely increases.When Li was added to the filler metal, and Mg was added to the corematerial, no effect was observed when the Sb content in the filler metalwas low (specimen 42), and the brazability decreased when the Sb contentin the filler metal was too high (specimen 43).

When Li, Bi, Sr, and Sb were added to the filler metal, and Mg was addedto the core material, an improvement in brazability was not observedwhen the Fe content, the Mn content, and the Ti content in the fillermetal were low (specimen 44 (as compared with specimen 18)), and thebrazability decreased when the Fe content, the Mn content, and the Ticontent in the filler metal were too high (specimen 45 (as compared withspecimen 18)).

Example 2

The following test was performed in order to determine the effects ofthe etching solution and the etching depth. In order to uniformly form afillet on each joint of a brazing target product in which a plurality oftypes of joints are present at a short distance, it is necessary tosufficiently break an oxide film on at least the surface of the fillermetal so that formation of a fillet is not hindered. In the clearancefilling test illustrated in FIG. 1 in which a fillet is formed at oneposition, physical breakage (mechanical breakage along with formation ofa fillet) of the oxide film efficiently proceeds when forming a filletdue to the effects of surface tension and the like. Therefore, a filletis easily formed uniformly (i.e., a fillet can be easily formed to havea length corresponding to the amount and the properties of the moltenfiller metal) even when the oxide film is insufficiently broken to someextent.

In order to more strictly evaluate the fillet-forming capability, atwo-dimensional clearance filling test that utilizes the clearancefilling test specimen illustrated in FIG. 6 was performed. The clearancefilling test specimen illustrated in FIG. 6 differs from the clearancefilling test specimen illustrated in FIG. 1 in that the verticalmaterial is replaced with a round tube. If the oxide film formed on thesurface of the filler metal is not sufficiently broken in a planarmanner (without anisotropy), formation of a fillet becomes non-uniform,and the clearance filling length decreases. Two-dimensional clearancefilling test: Specimen 19 (brazing sheet) that showed excellent resultsin the clearance filling test and the cup test in Example 1, and a 3003alloy tube were degreased, and subjected to an etching treatment using a5% NaOH solution (45° C. or 60° C.), a 1% hydrofluoric acid solution(20° C.), a 1% hydrofluoric acid+2% nitric acid solution (20° C. or 50°C.), or a 3% phosphoric acid+5% sulfuric acid solution (70° C.). Theimmersion time (5 to 300 seconds) was changed corresponding to theetching solution. The etching depth of the brazing sheet was calculatedfrom the GD-OES analysis results before and after the etching treatment.Specimen 19 (horizontal material) and the 3003 alloy tube (verticalmaterial) were assembled to prepare the two-dimensional clearancefilling test specimen illustrated in FIG. 6, and the clearance fillingtest specimen was brazed in the same manner as in Example 1. The resultsare shown in Table 3.

TABLE 3 Two- dimensional Etching clearance depth filling length SpecimenEtching solution (nm) (mm) 46 1% hydrofluoric acid 6 27 47 1%hydrofluoric acid 10 29 48 1% hydrofluoric acid 120 32 49 1%hydrofluoric acid + 2% nitric acid 5 27 50 1% hydrofluoric acid + 2%nitric acid 8 28 51 1% hydrofluoric acid + 2% nitric acid 100 31 52 1%hydrofluoric acid + 2% nitric acid 500 30 53 3% phosphoric acid + 5%sulfuric 9 26 acid 54 3% phosphoric acid + 5% sulfuric 70 29 acid 55 3%phosphoric acid + 5% sulfuric 110 28 acid 56 1% hydrofluoric acid 4 2157 1% hydrofluoric acid + 2% nitric acid 3 18 58 3% phosphoric acid + 5%sulfuric 3 14 acid 59 5% NaOH solution 5 11 60 5% NaOH solution 30 9 615% NaOH solution 120 13

As shown in Table 3, an etching depth of 5 nm or more was obtained, anda stable fillet was formed when the etching treatment was performedusing the acid solution (hydrofluoric acid solution, hydrofluoricacid+nitric acid solution, or phosphoric acid+sulfuric acid solution)(specimens 46 to 55). Even when the etching treatment was performedusing the acid solution, the shape of the fillet was unstable, and theclearance filling length decreased when the etching depth was less than5 nm (specimens 56 to 58). When the etching treatment was performedusing the NaOH solution, the shape of the fillet was unstable, and theclearance filling length was short irrespective of the etching depth(specimens 59 to 61).

Example 3

Specimen 19 (brazing sheet) that showed excellent results in theclearance filling test and the cup test in Example 1, and a 3003 alloytube were degreased, and immersed in a 1% hydrofluoric acid+2% nitricacid solution (20° C.) (etching treatment, depth: 100 nm). An oilsolution that decomposes when heated at 120° C. (n-paraffin-based oilsolution A), 200° C. (paraffin-based mineral oil solution B), 270° C.(polybutene-based oil solution C), 380° C. (naphthene-based mineral oilsolution D), or 450° C. (silicone oil-based oil solution E) in an inertgas, was applied to specimen 19 (brazing sheet) in an amount of 300mg/m², 500 mg/m², or 1400 mg/m².

Specimen 19 (brazing sheet) and the 3003 alloy tube were cooled to −10°C. in a freezer, placed in a thermo-hygrostat (temperature: 50° C.,humidity: 85%), removed from the thermo-hygrostat every day, cooled to−10° C. in the freezer, and returned to the thermo-hygrostat (i.e., dewcondensation was caused to occur once a day). A two-dimensionalclearance filling test was then performed in the same manner as inExample 2. The results are shown in Table 4. In Table 4, “0 days”indicates the results obtained when the brazing test was performeddirectly after applying the oil solution.

A case where the clearance filling length was 25 mm or more wasevaluated as “Acceptable” (“A” in Table 4), a case where the clearancefilling length was 19 mm or more and less than 25 mm was evaluated as“Fair” (“B” in Table 4), and a case where the clearance filling lengthwas less than 19 mm was evaluated as “Unacceptable” (“C” in Table 4).

TABLE 4 Decomposition Application Two-dimensional clearance fillinglength after storage Oil temperature in amount in thermo-hygrostat (withdew condensation) (mm) Specimen solution inert gas (° C.) (mg/m²) 0 days1 day 3 days 7 days 14 days Evaluation 62 A 120 300 32 21 8 0 0 A to C63 A 120 500 31 25 11 0 0 A to C 64 A 120 1400 31 26 17 6 0 A to C 65 B200 300 31 24 19 15 11 A to C 66 B 200 500 32 31 31 28 27 A 67 B 2001400 30 31 31 30 28 A 68 C 270 300 30 26 22 19 18 A to C 69 C 270 500 3031 30 30 29 A 70 C 270 1400 31 32 30 29 29 A 71 D 380 300 30 27 22 17 18A to C 72 D 380 500 29 28 26 27 25 A 73 D 380 1400 28 29 27 25 26 A 74 E450 300 22 18 12 14 10 C 75 E 450 500 18 15 14 9 5 C 76 E 450 1400 15 1410 5 0 C

As shown in Table 4, when the oil solution B, C, or D that decomposeswhen heated at 200 to 380° C. in an inert gas was applied (specimens 66,67, 69, 70, 72, and 73), a long-term deterioration suppression effectwas achieved (i.e., the effect of the etching treatment was maintainedfor a long time even in a severe storage environment) when theapplication amount was 500 mg/m² or more. When the oil solution B, C, orD was applied in an amount of less than 500 mg/m² (specimens 65, 68, and71), the effect of the etching treatment was maintained for a shorttime. When the oil solution A that decomposes when heated at atemperature of less than 200° C. in an inert gas was applied (specimens62 to 64), the effect of the etching treatment was maintained for ashort time.

When the oil solution E that decomposes when heated at a temperature ofmore than 380° C. in an inert gas was applied (specimens 74 to 76), thebrazability deteriorated upon application, and further deteriorated dueto the dew condensation treatment. It is considered that the oilsolution did not completely decompose during heating for brazing, andresidual oil adversely affected brazability.

What is claimed is:
 1. An aluminum alloy brazing sheet for brazingaluminum in an inert gas atmosphere without using flux, the brazingsheet comprising a core material and a filler metal, a first side or thefirst side and a side opposite to the first side of the core materialbeing clad with the filler metal, the core material being formed of analuminum alloy that includes 0.2 to 1.3 mass % of Mg, with the balancebeing aluminum and unavoidable impurities, the filler metal including 6to 13 mass % of Si and 0.004 to 0.1 mass % of Li, with the balance beingaluminum and unavoidable impurities, a surface oxide film having beenremoved from the brazing sheet, and an oil solution that decomposes whenheated at 380° C. or less in an inert gas having been applied to thebrazing sheet, wherein the decomposition temperature of the oil solutionis 200-380° C. and the application amount of the oil solution is atleast 500 mg/m².
 2. The aluminum alloy brazing sheet according to claim1, wherein the aluminum alloy that forms the core material includes 0.2to 1.3 mass % of Mg, and one or more elements from among 0.5 to 1.8 mass% of Mn, 1.0 mass % or less of Si, 1.0 mass % or less of Fe, 0.5 mass %or less of Cu, 0.5 mass % or less of Zn, 0.2 mass % or less of Ti, and0.5 mass % or less of Zr, with the balance being aluminum andunavoidable impurities.
 3. The aluminum alloy brazing sheet according toclaim 1, wherein the filler metal further includes one or more elementsfrom among 0.004 to 0.2 mass % of Bi, 0.05 to 0.4 mass % of Mg, 0.002 to0.05 mass % of Sr, 0.003 to 0.07 mass % of Sb, 0.05 to 0.8 mass % of Fe,0.05 to 0.2 mass % of Mn, and 0.01 to 0.15 mass % of Ti.
 4. The aluminumalloy brazing sheet according to claim 2, wherein the filler metalfurther includes one or more elements from among 0.004 to 0.2 mass % ofBi, 0.05 to 0.4 mass % of Mg, 0.002 to 0.05 mass % of Sr, 0.003 to 0.07mass % of Sb, 0.05 to 0.8 mass % of Fe, 0.05 to 0.2 mass % of Mn, and0.01 to 0.15 mass % of Ti.